Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 11 - Review - Exercises - Page 833: 12

Answer

(a) Vertex: $V(\frac{3}{2},-\frac{3}{2})$ Focus: $F(\frac{3}{2},-\frac{3}{4})$ Directrix: $y=-\frac{9}{4}$ (b)

Work Step by Step

Equation of a parabola with vertical axis and vertex at $(h,k)$: $(x-h)^2=4p(y-k)$ $x^2=3(x+y)$ $x^2-3x=3y$ $x^2-3x+\frac{9}{4}=3y+\frac{9}{4}$ $(x-\frac{3}{2})^2=3[y-(-\frac{3}{2})]$ $h=\frac{3}{2}$ $k=-\frac{3}{2}$ Vertex: $V(h,k)=V(\frac{3}{2},-\frac{3}{2})$ $4p=3$ $p=\frac{3}{4}$ The given equation can be obtained by shifting $x^2=3y$ right $\frac{3}{2}$ unit and downward $\frac{3}{2}$ unit. In this equation: Focus: $F(0,p)=F(0,\frac{3}{4})$ Directrix: $y=-p=-\frac{3}{4}$ Now, shift the focus and the directrix $\frac{3}{2}$ unit to the right and $-\frac{3}{2}$ unit downward: Focus: $F(\frac{3}{2},-\frac{3}{4})$ Directrix: $y=-\frac{9}{4}$
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